Add missing off_wait_time to light_onoff_brightness converter

[marazmarci]

I successfully used the onWithTimedOff command for relays and smart plugs in my automations. For some devices, it's enough only to provide an on_time value in the payload, but for some devices (such as the Sonoff ZBMINI, see note here), it's also required to provide an off_wait_time value. In Koenkk/zigbee2mqtt.io#2392, a documentation section was added for all devices supporting on_time about the "on with timed off" feature, in which it is mentioned that the device may require to also provide an off_wait_time value. This documentation section is also shown for lights (example), so as a user, I would expect it to work.

on_time works¹ for lights (I tried some IKEA LEDxxxxGx lights), but I noticed that off_wait_time produces the following error:

No converter available for 'off_wait_time' (0)

¹ "works" in the sense that it doesn't produce an error in Z2M. However, for some models, it actually works, but for some, it doesn't, that's why I started experimenting with off_wait_time.

In this PR, I added the off_wait_time key to the light_onoff_brightness converter. As far as I understand the code, this works when a brightness value is not provided, and light_onoff_brightness delegates to on_off, according to this part of the code:

zigbee-herdsman-converters/src/converters/toZigbee.ts

Lines 1152 to 1154 in 7e8a807

	if (brightness === undefined) {
	// Converting the type to a generic one so we can set readAfterWriteTime and state.brightness without errors
	const result = (await converters1.on_off.convertSet(entity, 'state', state, meta)) as KeyValueAny;

Some history: on_time was added to the same line of code in ef35333 by @Koenkk after @sjorge reported Koenkk/zigbee2mqtt#12276

[marazmarci]

@Koenkk, please add the hacktoberfest-accepted label to the PR. 🙏

[Koenkk]

Thanks!